The present invention relates generally to an illumination device, and more particularly, to a light guide illumination device in which light extraction structures are configured to produce a predetermined intensity pattern such as for use in a vehicle.
Optically transmissive materials, such as glass or polymers may be used as light guides to propagate light. A light guide typically includes at least one surface adapted to receive light from a light source and an optically smooth surface for reflecting light propagating through or along the light guide. Common examples of light guides include optical fibers traditionally used in the data communication industry and more recently light fibers used for illumination purposes. For example, U.S. Pat. No. 5,432,876 (the ""876 patent) discloses one such illumination device employing light fibers. In this device, light may be injected into at least one end of a light fiber and allowed to exit the fiber at a predetermined position or positions along the length of the fiber to produce an even illumination pattern. Light extraction structures or notches are formed in the core of the light fiber. The extraction structures define first and second reflecting surfaces, which reflect in a radial direction a portion of the light propagating axially through the fiber. The reflected light is directed at an angle that is less than the critical angle necessary for continued propagation along the fiber according to the principle of total internal reflection. As a result, the reflected light is extracted from the fiber. In contrast to prior techniques such as subjecting the fiber to relatively sharp bends, this system extracts light from the fiber in a controlled fashion.
Light fiber illumination devices have been proposed for use in automobiles and other vehicles. For example, they can be used to evenly distribute a point light source into a long, narrow line that may be employed in spoilers, along the edges of rear windows, or to follow the curve of a trunk lid. Examples of such devices may be found, for example, in U.S. Pat. Nos. 5,222,794, 4,811,172, 4,868,718, and 4,949,227.
Light fiber illumination devices can also be used as side markers, emergency flashers, and center high mounted stop lamps, which can serve as indicators of a vehicle""s features such as its overall length, width, and height. These devices often must meet specified standard requirements. For example, the Society of Automotive Engineers (SAE) sets forth a variety of different standards that recommend performance requirements for vehicle illumination devices, which define the amount, direction and distribution of light that the device should produce. For example, certain devices are required to provide light output over an angular range as large as +/xe2x88x9245 degrees for minimum vehicle conspicuity.
These requirements are often difficult or impossible to achieve with known light fiber illumination devices because they produce a limited set of intensity distributions which do not generally conform with any particular prescribed standard (i.e., SAE, etc.). This limitation arises because devices known in the art comprise light extraction structures that vary only in spacing and depth.
The present invention is therefore directed to the problem of providing an illumination device with light extraction structures that are appropriately configured to produce a predetermined illumination pattern, for example, one that may be uniform over a range of angles or that has a peak intensity at a given angle.
The present invention solves this problem by providing a light guide illumination device that has differently configured light extraction structures. A desired illumination pattern is achieved by individually tailoring the notch angle of each light extraction structure.
The present invention provides an illumination device that includes a light guide having a light guide core and an optically smooth surface for propagating light through the core. A light emitting region extends along a portion of the core and includes a plurality of light extraction structures distributed along the optically smooth surface. The light extraction structures are configured so that light reflected therefrom is emitted from the light guide through the optically smooth surface. At least two of the light extraction structures have different configurations from one another.
In one aspect of the invention, each light extraction structure includes an optically reflective surface extending into the light guide core and oriented at a notch angle to reflect light at an angle less than a critical angle so that light is emitted from the light guide through the optically smooth surface. The notch angle denotes the angle between the optically reflective surface and the axis perpendicular to the optically smooth surface.
In another aspect of the invention, the different configurations of the light extraction structures correspond to different notch angles.
In accordance with yet another aspect of the invention, the light guide may be a light fiber. Additionally, the light guide may have a circular or noncircular cross-sectional shape, and may even be a planar waveguide.
In accordance with another aspect of the invention, the plurality of light extraction structures have different configurations selected so that the emitted light forms a prescribed illumination pattern. The prescribed illumination pattern may be, for example, substantially uniform over an angular distribution of +/xe2x88x9245 degrees, or may be substantially non-uniform by providing relatively more intense light over an angular distribution of no more than about +/xe2x88x9210 degrees. xe2x80x9cAngular distributionxe2x80x9d is defined in relation to an essentially linear illumination device such as a light fiber, and means the distribution of light rays as a function of angle to some fixed direction. In the present case, light is emitted opposite from the side in which light extraction structures are formed, and this is defined as the direction of zero angle. Furthermore, this invention is primarily concerned with the angular distribution in the plane that contains the zero angle direction as well as the fiber axis. In addition to providing an illumination source that has pre-defined intensity levels when viewed by an observer, the prescribed illumination pattern may illuminate a target in a uniform or non-uniform manner. Therefore, available light is distributed efficiently to a target or to satisfy a prescribed standard. When employed as a vehicular illumination device, the prescribed illumination pattern may conform to an established standard for a vehicular illumination device.
In accordance with another aspect, the plurality of light extraction structures may be equally spaced apart from one another along the optically smooth surface. Alternatively, the plurality of light extraction structures may be unequally spaced apart from one another along the optically smooth surface.
In accordance with another aspect, the plurality of light extraction structures may be distributed along a plurality of longitudinal axes of a light guide. Preferably, a light guide in the form of a light fiber having two longitudinal axes may have light extraction structures having unequal notch angles and/or uneven notch spacing distributed along the axes.
In one particularly advantageous embodiment, the light guide is formed from a polymerizable material such as an acrylate, silicone, or urethane material.